> -----Original Message----- > From: Chuck Lever [mailto:[email protected]] > Sent: Monday, July 21, 2014 10:21 AM > To: Steve Wise > Cc: Devesh Sharma; Shirley Ma; Hefty, Sean; Roland Dreier; > [email protected] > Subject: Re: [for-next 1/2] xprtrdma: take reference of rdma provider module > > > On Jul 21, 2014, at 11:03 AM, Steve Wise <[email protected]> wrote: > > > > > > >> -----Original Message----- > >> From: Chuck Lever [mailto:[email protected]] > >> Sent: Monday, July 21, 2014 9:54 AM > >> To: Devesh Sharma > >> Cc: Shirley Ma; Steve Wise; Hefty, Sean; Roland Dreier; > >> [email protected] > >> Subject: Re: [for-next 1/2] xprtrdma: take reference of rdma provider > >> module > >> > >> Hi Devesh- > >> > >> Thanks for drilling into this further. > >> > >> On Jul 21, 2014, at 7:48 AM, Devesh Sharma <[email protected]> > >> wrote: > >> > >>> In rpcrdma_ep_connect(): > >>> > >>> write_lock(&ia->ri_qplock); > >>> old = ia->ri_id; > >>> ia->ri_id = id; > >>> write_unlock(&ia->ri_qplock); > >>> > >>> rdma_destroy_qp(old); > >>> rdma_destroy_id(old); =============> Cm -id is destroyed > >>> here. > >>> > >>> > >>> If following code fails in rpcrdma_ep_connect(): > >>> id = rpcrdma_create_id(xprt, ia, > >>> (struct sockaddr *)&xprt->rx_data.addr); > >>> if (IS_ERR(id)) { > >>> rc = -EHOSTUNREACH; > >>> goto out; > >>> } > >>> > >>> it leaves old cm-id still alive. This will always fail if Device is > >>> removed abruptly. > >> > >> For CM_EVENT_DEVICE_REMOVAL, rpcrdma_conn_upcall() sets ep->rep_connected > >> to -ENODEV. > >> > >> Then: > >> > >> 929 int > >> 930 rpcrdma_ep_connect(struct rpcrdma_ep *ep, struct rpcrdma_ia *ia) > >> 931 { > >> 932 struct rdma_cm_id *id, *old; > >> 933 int rc = 0; > >> 934 int retry_count = 0; > >> 935 > >> 936 if (ep->rep_connected != 0) { > >> 937 struct rpcrdma_xprt *xprt; > >> 938 retry: > >> 939 dprintk("RPC: %s: reconnecting...\n", __func__); > >> > >> ep->rep_connected is probably -ENODEV after a device removal. It would be > >> possible for the connect worker to destroy everything associated with this > >> connection in that case to ensure the underlying object reference counts > >> are cleared. > >> > >> The immediate danger is that if there are pending RPCs, they could exit > >> while > >> qp/cm_id are NULL, triggering a panic in > >> rpcrdma_deregister_frmr_external(). > >> Checking for NULL pointers inside the ri_qplock would prevent that. > >> > >> However, NFS mounts via this adapter will hang indefinitely after all > >> transports are torn down and the adapter is gone. The only thing that can > >> be > >> done is something drastic like "echo b > /proc/sysrq_trigger" on the > >> client. > >> > >> Thus, IMO hot-plugging or passive fail-over are the only scenarios where > >> this makes sense. If we have an immediate problem here, is it a problem > >> with > >> system shutdown ordering that can be addressed in some other way? > >> > >> Until that support is in place, obviously I would prefer that the removal > >> of > >> the underlying driver be prevented while there are NFS mounts in place. I > >> think that's what NFS users have come to expect. > >> > >> In other words, don't allow device removal until we have support for device > >> insertion :-) > >> > >> > > > > > > If we fix the above problems on provider unload, shouldn't the mount > > recover if the > > provider module is subsequently loaded? Or another provider configured > > such that > > rdma_resolve_addr/route() then picks an active device? > > On device removal, we have to destroy everything. > > On insertion, we'll have to create a fresh PD and MRs, which isn't done now > during reconnect. So, insertion needs work too. >
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